A perfect example of why you should never listen to rumors. just wait for the official statements. Is it really "that" important that you know info before an official word? You are potentially just setting yourself up for disappointment.

Sit back and play it cool. You will get all the official info soon enough. There is no need to go digging. A bit speculation is all good fun though.

Car customisation is in the game ;) I heard that and other details (which all turned out to be true) from a guy who knows a guy (this was at an event with loads of game developers, in Scotland, the guy who told me wasn't even meant to know, this was in 2009!). Also, it's clearly already in the engine in GTA4 and there were garages for it that never opened (my guess is they cut it out possibly for disk space or time saving, it's not a major feature).